2024 day 19 part 2.

bin/day2419.ml

@@ -31,14 +31,35 @@ let rec memoize_has_pattern pattern towels =
       x
 
 let has_match towels pattern = memoize_has_pattern pattern towels
+let memo2 = Hashtbl.create 1000
+
+let rec memoize_count_matches pattern towels =
+  let pattern_len = String.length pattern in
+  let rec has_pattern = function
+    | [] -> 0
+    | h :: t ->
+        let towel_len = String.length h in
+        if String.starts_with ~prefix:h pattern then
+          memoize_count_matches
+            (String.sub pattern towel_len (pattern_len - towel_len))
+            towels
+          + has_pattern t
+        else has_pattern t
+  in
+  match Hashtbl.find_opt memo2 pattern with
+  | Some x -> x
+  | None ->
+      let x = if pattern_len = 0 then 1 else has_pattern towels in
+      Hashtbl.add memo2 pattern x;
+      x
+
+let count_matches towels pattern = memoize_count_matches pattern towels
 
 let part1 (towels, patterns) =
-  List.filter
+  List.filter (has_match towels) patterns |> List.length
-    (fun p ->
-      let x = has_match towels p in
-      flush stdout;
-      x)
-    patterns
-  |> List.length
 
-let _ = Aoc.main towels_of_file [ (string_of_int, part1) ]
+let part2 (towels, patterns) =
+  List.map (count_matches towels) patterns |> List.fold_left ( + ) 0
+
+let _ =
+  Aoc.main towels_of_file [ (string_of_int, part1); (string_of_int, part2) ]